Thermionic valve circuits



. Dec. 15, 1941. BLUMLEIN 2,265,996

\ THERMIONIC VALVE CIRCUITS Filed April 22 I939 INVENTOR. ALA/V POWER BLUMLEIN ATTORNEY.

Fatenie cc. 1%, lddl TMRMIONIC VALVE 1 Alan Dower Blumleln, Eallng,

assignor to Electric & lvilcal Industries Limited, Hayes, Middlesex,

Great Britain London, England,

England, a company of.

Application Apr-i122, 1939 Serial No. 269,397 in Great Britain April 25, 1938 4 Claims.

The present invention relates to thermionic valve circuits.

It is an object of the present invention to provide improved means for the mixing of electrical signals. An additional object of the invention is to provide improved means for the production of pulses such, for example, as are required in television systems.

According to, one feature of the invention a thermionic valve circuit for mixing electrical signals is provided comprising two or more thermionic valves having their cathodes connected together and provided with a common cathode impedance, a set of electrical signals and means for applying said signals to the control electrode of one of said valvesand a second set of electrical signals for mixing with the first mentioned set of signals, and means mentioned set of signals to the control electrode of .another of said valves, the application of a set of signals to one of said valves causing, or tending to cause the cathode potential of said valve to vary and thus producing, or tending to produce. potential variations across said impedance, which potential variations are applied effectively between the cathode and the control electrode of another valve so that the sets of signals applied individually to said valves are efiectively mixed and appear as mixed signals in one or more of the anode circuits of said valves and wherein, in order to limit the amplitude of signals passed by any of said valves it is arranged that on the application toone'of said valves of signals having positive values exceeding a predetermined value beyond which limitation is required, the control electrode-cathode potential of another of said valves is brought to a point where the amplification of that valve is reduced or eliminated.

In one form of the invention, the circuit comprises two thermionic valves, and signals to be mixed are applied to the two control electrodes of said valves, and the mixed signals are derived from either anode circuit of said valves or in push-pull from both anode circuits.

According to another feature of the invention, a thermionic valve circuit for the generation of pulses is provided comprising onic valves having gether and provided pedance, a source of a pair of thermitheir-cathodes connected towith a common cathode imcontrolling signal pulsesnon-conducting or conducting, and means for applying to the other valve controlling signal pulses also having sharp leading edges and having a time relationship with the first mentioned pulses so as to cause the last mentioned valve to be rendered conducting or non-conducting and the previously conducting or non-conductin vvalve substantially non-conducting or conductfor applying the second ing, the arrangement serving to generate pulses having a duration substantially equal to the time interval between the pulses applied to the respective valves.

The arrangement according to this feature of the invention may be employed for measuring the time or phase relationship between two sets of pulses, the measure of the time or phase relationship .being a function of the duration of the pulses generated by the circuit. This feature of the invention may also be employed for generating pulses of a predetermined duration. In this case the two sets of controlling pulses are arranged to have a predetermined time relationship and preferably a single source of controlling pulses is employed and the predetermined time relationship is obtained by delay means.

In order that the said invention may be clearly understood and readily carried into efiect the having sharp leading edgesand means for app1ying said pulses to one of said valves so to cause that valve to be rendered conducting or nonconducting and the other valve substantially same will now be more fully described with reference to the accompanying drawing in which- Figure 1 is a circuit arrangement for mixing two sets oi electrical signals and Figure 2 is a, circuit arrangement for the generation of pulses.

Figure 1 shows two tetrode valves H and M with their cathodes joined together and connected to an impedance I3 (shown as a resistance) which'is connected to a source of negative potential. It is preferable that the value of the impedance l3 at allfrequencles'it is desired to mix is large compared with reciprocal of the mutual conductive of the valves 15 and 52, but this is not absolutelyv necessary if push-pull signals are not desired. One set of signals is app d o 'the input terminal it which is connected via a coupling condenser to the grid of valve H which has a suitable grid leak resistance. The set of signals to be mixed with the signals applied to terminal it is applied tothe input terminal H which isconnected via a coupling condenser to the grid of valve 12, also having a leak resistanca. Positive potentials are applied to the screening and H2 in the usual manner, and the biases on jthecontrol grids are arranged so that the valves the provision of time grids of the tetrodes ll that operate on substantially linear portions of their characteristics. The anodes of the valves are connected through separate anode impedances (shown as resistances) to suitable positive potentials and to output terminals I4 and I5. If a varying potential is applied to the terminal I6 the cathode potential of valve II tends to follow the potential of the grid of valve II. Similarly the cathode potential of valve I2 tends to follow the potential of the grid of valve I2. Assuming the potential applied to terminal It to be V1 volts, and the potential applied to terminal I? to be V2 volts, then the anode current change in one of the valves can be shown to be approximately (V1V2) g/2, where g is the mutual conductance of one valve, it being assumed that the valves are working on the linear portions of their characteristics and that the cathode impedance I3 is large compared with the reciprocal of g. The signals applied at I 6 and I1 are therefore mixed and the mixed output may be taken oil at I4 or I5, or at both in push pull. Provided the current in the impedance I3 is less than that passed by either valve at zero grid bias an excessive input to either It or I! will not cause grid current to flow, but will cause a limited output signal in one or other direction the whole of the current through I3 flowing through one of the valves. As the output depends on the dinerence of the potentials applied to the grids at I 6 and H, the inputs are relatively reversed in phase before mixing. It will be apparent that more than two valves may be used in such a mixing circuit where more than two signals are required to be mixed. For examplei'or mixing three signals three valves may have their cathodes joined to a common cathode resistance, the mixture being obtained in any of the anode circuits oi the valves.

Figure 2 shows a circuit for the production of a short pulse from longer controlling pulses which is a modification of Figure 1.- Parts in Figure 2 which correspond to similar parts in Figure 1 have been given the same reference numerals. The terminal I9 represents the input terminal to the grid of a valve 20, which acts as a cathode follower" valve, the resistance 2|, delay network I8 and terminating resistance 22 to allow for variation 5 volts tolerance. If the input acting as the cathode impedance. The input j terminals I6 and I1 01' the two valves II and I2 are connected to tappings on the delay network, which comprises series inductances and shunt capacitances connected in the normal manner. The purpose of the resistance 2I together with the cathode impedance of the valve 20 is to terminate correctly the delay network at the input end. The anode of valve 20 is connected to a source of positive potential. The valves II and I2 are triodes and the gridof valve II is biased negatively by a battery 23 and the grid of valve I2 is biased positively by a battery 24.

In order to explain the operation of the circuit of Figure 2' it will be assumed, for example, that it is necessary to produce so called line synchronising pulses for television purposes, the pulses being of, say, 10 micro-seconds duration. Positive controlling pulses 01' longer duration than 10 micro-seconds, which pulses may, for example, be line sawtooth waves (1; e. saw-tooth wave-forms occurring at line frequency) with a rapid stroke at the beginning of each saw-tooth wave are applied to terminal I9, and the pulses then travel along the delay network. The term i-, nals I6 and I! are tapped on the delay network valve I2 it switches this valve ,on and automatically switches ofi valve II. Thus a short pulse of 10 micro-seconds duration is produced. Actually a negative pulse is obtained at I 4 and a positive pulse is obtained at I5. The edges of the short pulse are determined by the leading edge of the waveform applied at terminal I9. After the leading edge has arrived at I! and turned off valve II, the trailing edge of the saw-tooth wave form will only bias valve II more negatively thus maintaining it in the off position.

Hence only the leading .edge of the wave-form applied at terminal I9 is of importance,,provided that there is an interval in excess of (in the Present example) 10 micro-seconds between the end of the pulse and the beginning of the next. As an example of the operation of a circuit such as Figure 2 suppose the resistance I3 passes 10 milliamperes and valves II and I2 are such that they. require 2 volts between grid and cathode in order to cause 10 m./a. to flow and 'l2 volts to cut off the anode current. If the grid of valve II is 12 volts with respect to its cathode and the grid of valve I2 is its cathode, then valve I2 will pass 10 m./a. and valve II will pass no current. A potential difference of l0-volts applied between the two grids (in such a sense as to bias valve I2 more negatively) will cause valve II to pass 10 m./a. and valve I2 to pass no current. In practice in order in valve characteristics the grid bias of valve II is made, say, 15 volts negative of the grid bias of valve I2 so as to allow at I 6 be 30 volts, then the leading edge will drive the grid 01' valve II to 15 volts more positive than the grid of valve anode-grid capacities of the valves may be neutralised if desired by cross coupled condensers from the anodes to the grids of the valves. A slight over neutralisation will tend to sharpen the pulse output. .As the valves are not working linearly irregularities may be produced by such neutralisation at the beginning and end of pulses so that screened valves are often preferable. The operation of Figure 2 has been described with reference to a control wave which has a sharp leading edge rising rangement may be equally well used with anegative sharp leading edge. In this latter case the biases of the valves are interchanged, valve II being normally conducting and valve I2 normally non-conducting. The negative pulse switches oil valve II first (thus switching on I2) and then switches off valve I2 restoring the circuit to its original condition.

The arrangement of Figure 2 may be used with with other pairs of valves to produce other pulses from the same delay network. Tappings for the from suitable places on 2 volts with respect to positively. The ar-.

mix pulses, such as those derived from frame freused to apparatus as shown in Figure 2, say, quency pulses. For example, the grid of valve I I (in Figure 1) may be biased more negatively than the grid of valve I2, so that valve H is normally cut off. Posi ive line frequency pulses (as derived from terminal IS in Figure 2) are applied to terminal IS with sumcient amplitude to turn valve II on and valve l2 off. Negative frame frequency pulses (derived, for example, by an arrangement such as Figure 2 with frame frequency control pulses and alonger delay period) are applied to terminal 11 and are of suflicient amplitude to switch valve l2 oil and valve H on (as for line pulses). The simultaneous occurrence of line andframe pulses gives an output signal at H or l5 of substantially the same amplitude as that given by either alone.

I claim:

1. Apparatus for producing a wave form of definite duration compris'ng a pair of thermionic tubes having anode, cathode and at least one control electrode, said cathodes being-electrically connected together, impedance means connected to said cathodes and common to the anode-cathode path of both of said tubes, a variable delay network, means connecting the control electrode of each of said tubes to a point on said delay network, and means for impressing an electric wave onto said delay network.

2. Apparatus in accordance with claim 1, wherein there is provided in addition an additional thermionic vacuum tube having anode,

cathode and at least one control electrode, and

having said time delay network connected in the anode-cathode path thereof as a cathode impedance.

3. Apparatus for combining a plurality of electric waves comprising at least two thermionic tubes, each having an anode, cathode, and at least on control electrode, said cathodes being electrically connected together, impedance means common to the control electrode-cathode paths and anode-cathode paths of said tubes, means for impressing one of said waves on the control electrode-cathode path of one of said tubes, means for impressing another of said waves on the control electrode-cathode path of the other ofsaid tubes, an impedance means connected in the anode-cathode path of each of said tubes, and means for deriving push-pull waves from said combined waves comprising output terminal means connected to each of said impedance means.

4. Apparat for producing a wave form of definite duration comprising a pair of thermionic tubes having anode, cathode and at least one control electrode, said cathodes being electrically connected together, impedance means connected to said cathodes and common ode path of both of said tubes, a delay network, means connecting the control electrode of each of said tubes to a point on said delay network, and means for impressing an electric wave onto said delay network.

ALAN DOWER BLUMLEIN.

to the anode-cath- 

